1. Field of the Invention
This invention relates to a porous waterproof film having both of gas-permeability and waterproofness and a process for producing the same.
2. Brief Description of the Prior Art
The prior art directed to porous waterproof film has mostly been carried out mainly by subjecting a gas-permeable film substrate to a coating process with a resin to form a resin film on the substrate and thereby impart a superior waterproofness thereto. However, according to such a process, it has been difficult to impart a sufficient gas-permeability and the resulting product has been difficult to be regarded as a substantially gas-permeable waterproof film, and further, dampness due to sweat and moisture excreted from the body at the time of its wearing has given a disagreeable feeling.
As a technique for solving this problem, a process referred to as wet coating process has been known. For example, Japanese patent application laid-open No. Sho 56-26076 discloses a process wherein a solution of an urethane polymer dissolved in a polar organic solvent is coated onto a substrate, followed by dripping the resulting material in a water bath to remove the polar solvent and thereby form a finely porous polyurethane film having a gas-permeability. However, the process has drawbacks that the production steps are complicated and the allowable ranges of the production conditions are narrow.
According to the process, since a polyurethane resin which is an expensive raw material is used and particular processing conditions and processing equipments are required, the resulting film is so expensive that the resulting product can be used only for limited high-class clothes; hence the product has a drawback that it cannot be used for example for disposable uses or similar uses.
An object of the present invention is to provide a porous waterproof film which is superior in both of the properties of gas-permeability and waterproofness.
Another object of the present invention is to provide a porous waterproof film which can be produced under simple processing conditions and using simple processing equipments.
Still another object of the present invention is to provide a porous waterproof film which can be produced at cheap cost and hence is suitable to disposable uses.
Further still another object of the present invention is to provide a porous waterproof film having superior mechanical strengths.
Still another object of the present invention is to provide a process for producing a porous waterproof film having the above-mentioned properties.